The invention relates generally to computer systems and, more particularly, to a riser assembly for coupling peripheral cards to a circuit board.
Computer systems, such as desktop computers, laptop computers, work stations, and servers, are well known in the art. These computer systems typically include a system board, or motherboard, secured within a chassis. Other components, such as a hard disk drive, floppy disk drive, CD ROM drive, one or more cooling fans, and a power supply, are also mounted within the chassis. A computer system may also include one or more built-in peripheral devices, including a keyboard, mouse, video display, and both serial and parallel ports.
A typical motherboard comprises a large printed circuit board having a number of components mounted thereon, including a processor coupled to a host or local bus, a chip set, system memory (e.g., SDRAM) coupled to a memory bus, and a Peripheral Component Interconnect (PCI) bus. See, e.g., PCI Local Bus Specification, Revision 2.2, and PCI-X Specification, Revision 1.0a. The chip set bridges the PCI bus with the local bus and also bridges the PCI bus to each of an Industry Standard Architecture (ISA) bus and a Small Computer System Interface (SCSI) bus, if present. See, e.g., SCSI-3. The chip set may also provide a system memory controller and bridge the memory bus to the local bus (as well as to the PCI bus). In addition, a motherboard typically includes input/output (I/O) connectors, floppy disk and hard disk drive connections, as well as circuitry for controlling any built-in peripheral devicesxe2x80x94e.g., hard disk drives, floppy disk drives, and CD ROM drives, as noted above.
Generally, one or more card connectors (also referred to as card slots or card sockets) are located on a motherboard, each card connector for receiving a peripheral card. A peripheral card (also referred to as an expansion card, expansion board, or daughterboard) is added to a computer system to enhance that system""s capabilities. For example, a peripheral card may provide a network interface, enhanced audio capability, or enhanced graphics. A peripheral card, as well as the card connector into which it is inserted for coupling to the motherboard, is typically PCI compatible or ISA compatible, such that the peripheral card (and connector) can be coupled to the PCI bus or ISA bus, respectively. Those of ordinary skill in the art will appreciate that peripheral cards and connectors may be manufactured or configured to meet other well known standards.
The PCI specification defines the PCI bus and a corresponding bus transfer protocol for interconnecting with any xe2x80x9cPCI devices.xe2x80x9d As used herein, the term xe2x80x9cPCI devicexe2x80x9d refers to any PCI compatible device, hardware, or component. Included in the PCI busxe2x80x94or integrated into the chipsetxe2x80x94is a bus arbitrator for evaluating pending requests by PCI devices for access to the PCI bus. Every PCI device (and the card connector coupling that device to the motherboard and, hence, to the PCI bus) includes a pair of arbitration lines connecting it directly to the bus arbitratorxe2x80x94a request (REQ#) line and a grant (GNT#) line. When a PCI device requires use of the PCI bus for a transaction (e.g., a data transfer), that device asserts a REQ# signal on its request line. When the bus arbitrator has determined that the requesting PCI device should be granted control of the PCI bus, it asserts a device-specific GNT# signal on the grant line of the requesting device. Any transactions conducted across the PCI bus, including bus arbitration, are generally synchronized to a PCI clock (PCI CLK) signal. During a transaction performed by a PCI device, the PCI device may assert or receive a number of other signals, including address and data signals, interrupt requests, and transaction control signals. Thus, every PCI device must be coupled (via its corresponding card connector or other interface) to the PCI bus by a plurality of signal lines.
The manufacture of motherboards is highly standardized, and a motherboard may be fabricated according to any one of a number of common specifications. For example, a motherboard may be manufactured in accordance with the ATX specification (see ATX Motherboard Specification, Release 2.03, December 1998), the microATX specification (see microATX Motherboard Interface Specification, Version 1.0, December 1997), or the NLX specification (see NLX Motherboard Specification, Release 1.8, April 1999), as well as other specifications. Motherboards meeting one of these specifications are readily available in the market. Customized motherboard configurations are generally available; however, non-standard board layouts are less preferred due to higher production costs.
There is presently an increasing demandxe2x80x94in applications such as rack mounted servers and portable computersxe2x80x94for computer systems and chassis exhibiting a low profile or small xe2x80x9cform factor.xe2x80x9d As used herein, the term xe2x80x9cform factorxe2x80x9d refers generally to a height or thickness of a computer system or chassis relative to its lateral dimensions. Thus, depending on its orientation within a chassis, the xe2x80x9cform factorxe2x80x9d of a motherboard may be its relative height dimension as measured transverse to the plane of the motherboard. To satisfy the demand for such low profile computer systems, manufacturers must provide motherboard assemblies exhibiting a small form factor and adapted for mounting in a small form factor chassis. However, card connectors are typically mounted to a motherboard such that a peripheral card inserted into the card connector is oriented transverse to the plane of the motherboard. When installed, a peripheral card can extend a relatively great distance above a motherboard, making the motherboard assembly incompatible with a small form factor chassis.
To adapt a motherboard assembly having a plurality of peripheral cards coupled theretoxe2x80x94at least some of which peripheral cards violate the form factor of the intended chassisxe2x80x94it is known in the art to use a riser card. A typical riser card comprises a low profile circuit board adapted for insertion into a card connector on the motherboard and having a plurality (e.g., three) of secondary card connectors mounted thereon, each of these secondary card connectors providing a point of insertion for mounting a peripheral card parallel to the plane of the motherboard. Such a riser card assembly can provide a low profile motherboard assembly capable of fitting within a small form factor chassis; however, additional conductors or other communication paths must be routed to the card connector that receives the riser card to provide signal lines (e.g., the REQ#, GNT#, and PCI CLK signals, as well as others) for any peripheral cards in excess of one. Thus, a customized motherboard must be designed and manufactured to accommodate the riser card and requisite signal lines and, as noted above, such customized motherboards increase manufacturing costs.